Not a hard problem once you see it as a simple scan and merge intervals kind of thing.
Clarify the input format and edge cases, then propose a single-pass linear scan that tracks the start of each above-threshold period and emits it when the intensity drops to or below the threshold. Discuss time/space complexity and test with boundary cases like all above, all below, and alternating values.
Pro tip: Mention that you would confirm whether the threshold is inclusive or exclusive and how to handle missing timestamps or irregular intervals, as these details often matter in production systems.
Ask about input format, threshold inclusivity, handling of empty lists, and whether timestamps are sorted or have gaps.
Propose a single-pass approach that iterates through entries, starting a period when intensity exceeds the threshold and ending it when it falls below.
Ensure the last period is closed if the list ends while above threshold, and define the output format (e.g., list of [start, end] timestamps).
State O(n) time and O(1) extra space (excluding output), and walk through test cases like all above, all below, and alternating values.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.